I. Field of the Invention
The present invention relates to a system for monitoring selected engine components of an internal combustion engine as well as controlling selected engine components to optimize engine operation and reduce exhaust emissions.
II. Description of the Prior Art
The operation and exhaust emissions of internal combustion engines of the type used in automobiles and trucks are dependent upon the air/fuel (A/F) ratio of the engine. These operational characteristics are typically expressed as a function of the air excess ratio .lambda. which is defined by the following equation: ##EQU1## where A/F.sub.st is the stoichiometric air/fuel ratio.
With reference now to FIG. 1 which illustrates the air/fuel (A/F) ratio versus engine emissions, a lean A/F mixture (.lambda.&gt;1) results in lower carbon monoxide and hydrocarbon emissions in the exhaust emission, but higher concentrations of nitrous oxides (NOx). Conversely, a rich A/F ratio operating condition (.lambda.&lt;1.0) results in greater engine power but also higher carbon monoxide and higher hydrocarbon emissions. However, during a rich engine operating condition, the concentration of nitric oxides is reduced.
Still referring to FIG. 1, the concentration of oxygen (O.sub.2) in the exhaust emissions is very small for values of .lambda.&lt;1.0. These small concentrations of oxygen occur because substantially all of the oxygen is combusted with the fuel during a rich engine operating condition. Conversely, the concentration of oxygen in the exhaust emissions increases during a lean engine operating condition (.lambda.&gt;1) since there is insufficient fuel to totally combust with the oxygen.
In order to reduce the concentration of noxious emissions in the exhaust emissions from internal combustion engines, it has been previously known to use a three way catalytic converter (TWC) in series with the exhaust combustion products from the internal combustion engine. Such three way converters effectively reduce the amount of hydrocarbons, carbon monoxide and NOx in the exhaust emissions from the engine.
One limitation of the three way catalytic converters, however, is that they operate efficiently only in a very narrow band centered around the stoichiometric A/F ratio (.lambda.=1). Consequently, in order for the engine emission control system for these previously known systems to operate effectively, the emission control system must determine if the A/F mixture is at the stoichiometric point. If not, the three way catalytic converter will not adequately remove the noxious engine emissions from the engine exhaust.
In order to determine engine operation at the stoichiometric A/F mixture, these previously known engines have utilized an oxygen sensor, also known as a .lambda. sensor, which is operatively positioned in the exhaust gas stream from the engine. These previously known oxygen sensors produce a first output signal in the absence of oxygen in the exhaust gas stream and, conversely, produce a second signal when oxygen is detected in the exhaust gas stream from the engine. Consequently, the presence of the first signal from the oxygen detector is an indication that the engine is operating with a rich A/F mixture since there is an absence of oxygen in the exhaust gas stream while, conversely, the presence of the second signal from the oxygen sensor is indicative of a lean A/F mixture due to the presence of oxygen in the exhaust gas stream.
Thus, while these previously known oxygen sensors have been adequate for determining whether the engine was operating with a rich or lean A/F mixture, such oxygen sensors were inadequate for determining the actual value of .lambda. and thus the degree of richness or leanness of the air/fuel mixture. Determination of the actual value of .lambda., however, would be highly advantageous in order to optimize the engine operation as well as reduce undesirable engine emissions.
A still further disadvantage of these previously known engine control systems is that no provision was made in such control systems for monitoring the operation of the various engine components and especially those components involved in the reduction of undesirable engine emissions. Consequently, deterioration or complete failure of an engine component, such as the three way converter, would result in the unacceptable exhaust of noxious engine emissions from the engine and yet be undetected by the control system for the engine. Likewise, none of these previously known systems incorporate any means for monitoring the status of the various sensors used both in the control of the engine combustion as well as in the reduction of undesirable engine emissions.